Electromagnetic switch



Feb. 16, 1965 E. LAWRENCE ETAL 3,170,054

ELECTROMAGNETIC SWITCH Filed June 9, 1961 3 Sheets-Sheet 1 ATTORNEY Feb. 16, 1965 Filed June 9,

L E. LAWRENCE ETAL ELECTROMAGNETIC SWITCH 3 Sheets-Sheet 2 INVENTORS LELAND E. LAWRENCE JOHN L. HAYDU ATTORNEY Feb. 1965 E. LAWRENCE ETAL 3,

ELECTROMAGNETIC SWITCH Filed June 9, 1961 3 Sheets-Sheet 3 37 5a 7 so 447 40 4'0 32 3 4 5, "F 3/ T "2o' a: 2'1 33 I M35 50 54 3 5 8 8 5 2a 6 25 3o 47 a2 I 32 INVENTORS LELAND E. LAWRENCE JOHN L. HAYDU Qzm AT TORNEY United States Patent 3,170,054 ELECTROMAGNETIC SWITCH Leland E. Lawrence, Wauwatosa, and John L. Haydn, Milwaukee, Wis., assignors to Allen-Bradley Company,

Milwaukee, Wis., a corporation of Wisconsin Filed June 9, 1961, Ser. No. 116,156 11 Claims. (Ci. 200-447) This invention rel-ates to electric switches, and it more particularly resides in a switch having an improved contact assembly which provides for more effective contact operation and increased contact life.

Switch contact operation, comprising contact movement during closing of the switch, retreat of the contacts during opening the switch and interrupting the current, and the slight movements of contacts while in closed position, is a basic factor in determining the effectiveness and life of any electrical switch. The development of the present invention has been directed primarily toward answering problems relating to contact operation, and investigations in connection with the development have shown that contact movements after initial engagement are perhaps the most detrimental factors in reducing the effectiveness of contacts and in shortening contact life. Arcing encountered in opening the contacts is also, of course, a prime factor in determining contact life, and probably more work has heretofore been done in the area of are prevention and extinguishment than in any other phases of contact operation.

Contact movements after initial engagement reduce contact life primarily because of the rough, friable surfaces developed on contacts, even after short periods of use, by oxidation due to heating and arcing. When contacts that have developed such surfaces are brought together and then allowed to bounce, rock, wipe or slide across one another, an abrasive grinding action results that causes the contact surfaces to wear and erode thereby reducing contact life.

Contact movement after initial closure is also responsible for other deleterious effects. For example, bouncing or rebound of the movable contacts during closure causes spasmodic currents which increase arcing erosion to thereby reduce contact life and increase the possibility of welding or overheating the contacts. Further, movement in the nature of rapid minute oscillations of the contacts While closed, referred to herein as the Trevelyan effect and characterized by the presence of a high pitched singing noise, is accompanied by a rise in the temperature of the contacts. Still further, any slight movements of the contacts after closure can result in local arcing that causes welding of the contacts.

Accordingly, it is a general object of this invention to provide a contact assembly for an electromagnetic switch which eliminates or reduces to a minimum relative movement of the contacts after initial closing engagement. the preferred embodiment of the invention, this is accomplished by the cooperative and complementary action of a number of structural features. First, the movable Contact spanners and the switch actuator are constructed and arranged to provide saddle-like guides for the movable contacts that seat the contact spanners in the saddlelike guides each time the switch is opened thus disposing the movable contacts in an aligned position, longitudinally, rotationally and laterally, prior to contact closure. The guides are so constructed as to provide a substantial bearing area between the contact spanners and guides to increase their effectiveness and to reduce wear on the switch elements. Upon each closing action, the aligned movable contacts will necessarily engage the stationary contacts in the same manner to provide a uniform initial engagement. The saddle-like guides are, however, effective for seating and positioning the movable contacts only when the contacts are opened, and as soon as an initial closing engagement is made the movable contacts are freed from the saddle-like guides to permit relative movement with respect to the actuator during the remainder of the closing movement of the actuator and the magnet that propels the actuator. A free-floating mounting is thus provided for the movable contacts as soon as initial closure is made to render the movable contacts substantially independent of the actuator.

Another feature of the invention is the use of movable and stationary contacts that are disposed obliquely rather than being normal to their path of travel. This construction provides a horizontal force component for the movable contacts which serves to inhibit contact bounce and also serves to dampen Trevelyan efiect oscillations. Further, the oblique placement of the contacts can be utilized to advantage in switch design for space saving purposes. In the preferred embodiment of the invention, an angle of obliqueness is selected that provides for the foregoing advantages while preventing a wedging action that might lead to the building up of shoulders on the contacts after repeated action or which might cause a failure to open properly.

Still another feature of the invention is the use of contact surfaces of selected face configuration to provide a stable three point engagement between the movable and stationary contacts to prevent relative movement and to insure effective electrical contact.

Another feature of the invention is the use, in connection with contacts and terminals having a conventional magnetic blowout configuration, or contacts that are relatively narrow as compared to their length to increase the strength of the magnetic blowout field.

It is, therefore, a specific object of this invention to provide an electromagnetic switch contact assembly that incorporates the foregoing features.

It is another object of this invention to provide a contact assembly that has greater life than contact assemblies found in previous switches.

It is another object of this invention to provide a contact assembly that may advantageously employ a cadmium-oxide silver alloy for the contacts.

It is another object of this invention to provide a switch contact assembly that has enhanced arc extinguishing characteristics.

It is a further object of this invention to provide a switch assembly that occupies a minimal amount of space.

It is another object of this invention to provide a switch assembly that is of relatively simple and inexpensive construction while being rugged enough to withstand long continued use.

Other objects and advantages of this invention will appear from the description to follow. In the description reference is made to the accompanying drawings, forming a part hereof, in which there is shown, by way of illustration and not of limitation, a specific embodiment of the invention.

In the drawings:

FIG. 1 is a front view in elevation, with parts broken away and in section, of an electromagnetic switch containing a contact assembly formed according to this invention,

FIG. 2 is a view in cross-section, with parts broken away and in section, of the switch of FIG. 1 taken through the plane 2-2 shown in FIG. 1,

FIG. 3 is an enlarged fragmentary view in cross-section of the switch of FIG. 1, with the movable contacts thereof shown in open position,

FIG. 4 is a view similar to FIG. 3 but with the movable contacts in closed position.

FIG. 5 is a fragmentary view in cross-section taken through the plane 5-5 shown in FIG. 4,

FIG. 6 is a view in cross-section taken through the plane s s shown in FIG. 3,

FIG. 7 is a view in cross-section of the contacts of the switch taken through the plane 7-7 shown in FIG. 4,

FIG. 8 is a view in cross-section of the contacts of the switch taken through the plane 8--8 shown in FIG. 4, and

FIG. 9 is a fragmentary, enlarged view in perspective showing one of the front stationary contacts of the switch of FIG. 1.

The switch of FIGS. 1 and 2 includes a vertical mounting plate 1 formed of sheet material and having suitable apertures 2 for mounting on a panel or in an enclosure as desired. A cast metal frame 3 which may be constructed, for example, of diecast aluminum is secured to the plate 1 by rivets 4 and includes forwardly extending arms 5 that receive opposite ends of a yoke mount 6 which passes through a laminated yoke 7. The yoke 7 is thereby mounted on the frame 3, and forms the stationary part of an operating magnet.

A movable contact actuator 8, preferably molded of a plastic material such as a phenolformaldehyde, is slidably held by the frame 3 for vertical movement, and includes side arm portions 9, a foot portion 1%) and a crossbar portion 11. Forwardly extending portions 12 of the frame 3 serve to limit the downward motion of the actuator 8. A magnetic, laminated anmature 13 is held securely to the foot portion 12 by a spacer 14 and a resilient flat spring 15. The armature 13 cooperates with the yoke 7 to form a magnetic circuit and is moved upward into engagement with the yoke 7 upon energization of a coil 16. The coil 16 includes windings disposed about the facing poles of the armature 13 and yoke 7 and is seated by the frame 3 directly beneath the arms 5. A molded cover 17 is secured to the frame 3 by bolts 18 and serves to mount the front of the coil 16 and to enclose and retain the magnet members and the actuator it in place. The foregoing electromagnet elements of the switch of FIGS. 1 and 2 have not been described in detail since they form no part of this invention, and the contact assembly hereinafter described can be combined with a variety of magnetic actuators or devices of differing form.

In the particular switch of FIGS. 1 and 2, a set of three movable contact cages 19 that are integrally molded portions of the actuator 8 extend upwardly from the crossbar 11. Each cage 19 includes a pair of side walls 20, a top 21 and a floor 22. A spring seat 23 is provided on the floor 22 that serves to hold one end of a compression spring 24. The lower edges of the top 21 are beveled, as shown in FIGS. 24, to present downwardly and outwardly facing seating surfaces 25 that are oblique to the direction of actuator movement. As shown in FIGS. 1 and 5, the contact cages 19 are further characterized by fillets 26 at the juncture of the side walls 20 and the top 21 which have slopes converging upwardly toward one another so that the distance between side walls 20 decreases at the top of the cage openings.

A movable contact spanner 27, formed of a suitable conductive material of generally rectangular cross-section, is mounted in each cage 19. Although there are three sets of spanners 27 and cages 19 in the particular switch shown, only one set will be hereinafter described for purposes of simplicity, and it should be understood that all three sets are substantially identical. The spanner 27 includes a depressed central section 28 in which is formed a spring seat 29 whch holds the upper end of the spring 24, the spring 24 thus acting to bias the spanner 27 upwardly. At each end of the central section 28 there are upwardly extending portions 30 which are oblique to conform to the beveled surfaces 25 of the top 21. As seen in FIG. 5, the width of the spanner 27 at the central portion 23 is substantially less than the distance between the side-walls 219, and is slightly less than the distance between the uppermost portions of the fillets 26 where they merge with the top 21.

The central section 28 and the portions 30 of the spanner 27, together with the beveled surfaces and fillets 26 of the cage 19, cooperate to provide a saddle-type guide means to seat the spanner 27. As can be seen in FIGS. 3 and 4, when the contact bias spring 24 has moved the spanner 27 to the top of the cage 19, this condition occurring when the switch is opened, the beveled surfaces 25 and portions cooperate to center the spanner 27 axially, and the fillets 26 and the central portion 23 cooperate to center the spanner 27 transversely. Furthermore, all of these elements cooperate to center the spanner 27 rotationally. Still further, the spanner 27 is seated along substantially the entire area of the top 21 and surfaces 25 to provide an adequate bearing surface for proper seating and increased wear resistance. Each time the switch is opened, the spanner 27 is seated in a substantially identical position so that it is orientated for contact closure. As will be more fully described hereinafter, however, the spanner 27 is freed from engagernent with the walls of the associated cage 19 immediately upon initial contact closure to have a free-floating mounting.

The spanner 27 terminates at each end in downwardly oblique contact carrying portions 31 on which are mounted movable contacts 32 of any suitable composition. It is a particular advantage of this invention, however, that both the stationary and movable contacts may be of a cadmium-oxide silver alloy which has superior antiwelding ohracteristics. This material can be used since mechanical wear of the contacts is reduced in the practice of the invention. For reasons discussed hereinafter, the oblique angle of the contacts 32 should be approximately 15 to 30 degrees from a perpendicular to the path of the actuator 1%.

Referring again to FIGS. 1 and 2, an arc chamber 33 is attached to the frame 3 and includes a top or hood portion 34- and a rear closure member or spacer 35 that are both attached to the frame 3 by bolts 36. A front closure member 37 that is generally L-shaped in cross section, as viewed in FIGS. 24, is attached to the hood portion 34 by bolts 38. The hood portion 34 includes partitions 39 that serve to separate individual sets of contacts, and also closes the bottom of the chamber 33, as well as the front, with a clearance fit about the contact cages 19. The rear closure member 35 also fits up closely to the cages 19 to cooperate with the member 37 in substantially closing off the bottom of the chamber 33.

Generally U-shaped arc shields 40 of a thermal conductive metal are mounted on the hood portion 34 and member 37 by rivets 41 and surround each set of contacts to assist in arc extinguishment in a manner to be hereinafter described. The partitions 39, shields 49 and other portions of the chamber 33 are so arranged to reduce the space surrounding the contacts since it has been found that excessive space around the contacts makes arc extinguishment more difficult. This is believed to be due to the larger quantities of heated, ionized air which will then be developed during current interruption and which serve to maintain an arc. With the reduced spacing of this invention, arcs are generally extinguished completely the first time the current passes through zero value. The optimum construction places the bottom of the arc chamber immediately beneath the movable contacts when in open position and at the immediate lower ends of the shields 40.

Rear stationary contact members 42 extend through the hood 34 and are clamped securely in place by means.

ports 43, primarily serve as means to effect auxiliary connections. Bolts 46 serve to connect the upper ends of the members 42 and supports 43 and also serve to mount terminals 47 provided with set screws 48 for line connec-- tions. The inner ends of the contact members 42 carry tacts 49 are spherical as seen in FIGS. 2 and 8.

5 rear stationary contacts 49 that are disposed at an angle matching that of the rear movable contacts 32.

Front stationary contact members 50 pass between the hood 34 and front closure member 37 and are secured to the hood 34 by bolts 51 and supports 52. Bolts 53 connect the outer ends of the members 50 and 52 and also mount terminals 54 having set screws 55 for line connections. The terminals 54 are lower than the terminals 47 for easy access from the front of the switch. At their inner ends, the members 50 carry front stationary contacts 56 that are at an angle matching that of the front movable contacts 32.

The front contact members 50 are bent back upon themselves to present a loop for the current path at the contacts which will produce a magnetic blowout. The rear contact members 42 are also constructed to develop a magnetic blowout, and for both front and back contacts the configuration acts in the usual manner, upon opening the switch, to create a magnetic flux that tends to move the arcs outwardly.

Upon opening the switch, magnetic flux paths are created that loop around the contacts 32, 49 and 56. The arcs resulting from opening are blown outwardly by the magnetic flux so as to travel toward the associated channel, or U-shaped, shields 40 through ambient air which is apparently kept relatively cool by the close proximity of the shields 4i). A minimum of ionization is thus established by the arcs, and the air surrounding the arcs is cooled to deionize the region so that, as a result, the arcs are usually extinguished upon the currents initial passage through Zero value. For this purpose the shields 40 are closely spaced about the contacts, and in the embodiment shown a distance of only approximately five thirty-seconds of an inch from the contacts 32, 49 and 56 has been found satisfactory for extremely effective arc extinguishment. Such spacing has also been shown to be effective in switches of varying sizes and for the practice of the invention the spacing in any size switch should be approximately within the range of 0.4 to 1 times the maximum contact gap, and preferably at a value of 0.6 times the maximum contact gap.

Arc extinguishment by magnetic blowout is further enhanced by the configuration of the contacts 32, 49 and 56 which are generally rectangular with the longer dimension extending axially of the spanner as seen in FIG. 6. Thus, theflux path that encircles each of the opening contacts. will have a shorter length and reduced relucment between the movable contacts 32 and the stationary contacts 49 and 56 to minimize rocking or wiping motion and, therefore, in the embodiment of the invention shown herein, the movable contacts 32 are fiat, thefront stationary contacts 56 are cylindrical withltheir longitudinal axes transverse to the length of the spanner 27,

as-seen in FIGS. 2, 7 and 9, and the rear stationary consurfaces of the contacts 32, 49 and 56 were perfectly smooth, each. front stationary contact 56 would engage its associated movable contact 32 along the full length of aline A-Af parallel to the longitudinal axis of the If the referred to herein as the Trevelyan effect.

tacts that appear perfectly smooth have minute surface imperfections. Also, wear due to repeated operations or pitting due to electrical arcing may cause imperfections to be formed after the switch is in use. At all times, therefore, the line A-A' for each front stationary contact 56 can be considered to be a succession of points some of which are higher than others. For each contact 56, actual engagement with its associated contact 32 will be at the two highest points on the contact 56. Because of the cylindrical configuration of the contact 56, these two points will in all cases be on or very close to the line A-A. Similarly, due to the spherical configuration of the contacts 49, the point at which each of them engages its associated contact 32 will be at or very close to the center of the contact 49. In all cases, therefore, the front stationary contacts 56 will contact their associated movable contacts 32 at two points along a line that is generally transverse to the length of the spanner 27 and the rear stationary contacts 49 will contact their associated movable contacts 32 at points near the centers of the contacts 49. This gives rise to a stable, tripodal form of engagement for each contact spanner 27. It will be obvious, however, that spherical and cylindrical surfaces could be provided for the movable contacts while fiat surfaces are provided for the stationary contacts or that other variations could be made without departure from the invention.

It has also been found that the spanner 27 and the bias spring 24 should have a relatively high force-weight ratio in order to reduce or eliminate contact bounce upon closing by reducing the momentum of the spanner 27 while increasing the opposing force of the spring 24. Again, however, mechanical strength and current capacity must be taken into account in determining the proper size and weight of these elements.

When the switch of FIGS. 1 and 2 is in its open position, as seen in FIG. 2, the actuator 8 andarmature' 13 have assumed a downward position. The cages 19 have been moved downwardly with the actuator 8, thus moving the movable contacts 32 away from the stationary contacts 49 and 56 into an open position. The springs 24 have urged the spanners 27 into an aligned position axially, transversely and rotationally as hereinbefore stated. When an energizing current is then passed through the coil 16, the armature 13 is attracted toward the yoke 7 to move the actuator 8 and cages 19 upwardly. The first increment of this movement brings the movable contacts 32 into the forementioned three point engagement with the stationary contacts 49 and 56'. Immediately after initial engagement, the movable contacts 32 have a natural tendency to bounce or rebound and such movements are minimized due' to the high force-weight ratio of the spanners 27 and'springs 24-and the oblique placement of the contacts 32, 49 and 56 which provide for resulting horizontal force components that detract from the vertical momentum of the spanners 27. Al-

though the effect of the oblique placement may be somewhat increased as the angle of obliqueness is increased, too great an angle can cause shoulders to be built up on the contacts after repeated closings or can cause a wedging action that may prevent proper opening. Therefore, the aforementioned angle of approximately 15 to 30 degrees has been selected as most satisfactory.

In many older switches, the movable contact spanners have a tendency to rock or oscillate about their longitudinal axes during closing or in use which movement is accompanied by a rise in contact temperature and an undesirable singing noise. This is believed to be due to temperature effects and has been previously and is Such rocking is inhibited or eliminated by the oblique arrangement of the contacts 32, 49 and 56 of this invention since any such motion must be accompanied by a slide component that tends to damp it.

After the first increment of closing, there is an overtravel of the actuator 8 whereby it continues to move upwardly while the movable contacts 32 are stopped by their engagement with the stationary contacts 49 and 56. As the actuator 8 and cages 19 continue their upward movement, the spanners 27 are in efiect moved down wardly to the position of FIGv 4 and, therefore, out of engagement with the beveled edges 25 and the fillets 26. The spanners 27 are then supported only by the springs 24 to have the desired free-float. The spanners 27 and movable contacts 32 are thus, after the first increment of closing, substantially independent of any forces which might otherwise be transmitted through or by the actuator 8. In other words, should the travel of the actuator S be subject to variation or should there be shocks transmitted to the actuator 8 these will not be transmitted to the movable contacts 32 to cause any detrimental sliding or wiping movement.

Upon opening, when the current flow through the coil 16 is stopped, the actuator 8 and therefore the movable contacts 32 fall out of contact both in reference to the contact spring force and by means of gravity. Arcs resulting from opening are extinguished by the magnetic blowout which is enhanced by the rectangular configuration of the contacts 32, 49 and S6. The spanners 27 are again centered as hereinbefore described to be in position for a subsequent closing.

To summarize, this invention includes a number of features the primary effects of which are to minimize contact movement after closure, to provide improved arc extinguishment and to save space. It will be obvious, however, that a number of modifications might be made in the preferred embodiment shown and described herein and, therefore, the invention is not intended to be limited except insofar as such limitations appear in the following claims.

We claim:

1. In a switch contact assembly, the combination comprising: a contact actuator having a contact cage with spaced side walls and a top extending therebetween, said top having downwardly and outwardly facing beveled seating surfaces along opposite lower sides thereof, said side walls having fillets at their inner faces immediately below the junction with the top which converge upwardly toward one another to taper the spacing between the side walls to a narrower dimension at the top; stationary contacts on opposite sides of the contact cage; and a movable contact spanner inserted in the cage extending between the side walls and beneath the top with its ends in facing relation with the stationary contacts, said spanner being of a width at its portion between the side walls slightly less thanthe narrowest distance between the fillets and substantially less than the distance between the side walls below the fillets, and having a central depression with upwardly and inwardly facing surfaces that mate with the beveled seating surfaces of the top.

2. In a switch contact assembly, the combination comprising: an actuator having a contact cage comprising spaced side walls and a top extending therebetween, said top having downwardly and outwardly facing beveled seating surfaces along opposite lower sides thereof, said side Walls having fillets on their inner faces immediately below the junction with the top which converge upwardly toward one another to taper the spacing between the side walls to a narrower dimension at the top; a pair of spaced stationary contact members on opposite sides of the cage each having a downwardly and outwardly oblique con ducting portion terminating in a stationary contact; a movable contact spanner that is inserted in the cage and extends beneath the top and between the side walls having a depressed central portion with upwardly and inwardly facing surfaces that mate with the beveled sur faces, said central portion being of a width slightly less than the narrowest distance between the fillets and substantially less than the distance between the side walls below the fillets, said spanner terminating at each end in downwardly and outwardly oblique conducting portions on opposite sides of the cage that are each disposed at an angle approximately matching the angle of the oblique portion of the corresponding stationary contact member and each of which bears a movable contact facing a corresponding stationary contact, and resilient bias means to bias the spanner toward the top of the cage.

3. In a switch contact assembly, the combination comprising: a vertically movable actuator having a contact cage comprising spaced side walls and a top extending therebetween, said top having downwardly and outwardly facing beveled seating surfaces along opposite lower sides thereof, said side walls having fillets on their inner faces immediately below the junction with the top which converge upwardly toward one another to taper the spacing between the side walls to a narrower dimension at the top; a pair of spaced staionary contact members on opposite sides of the cage each having a downwardly and outwardly oblique conducting portion bearing a stationary contact; a movable contact spanner that is inserted in the cage and extends beneath the top and between the side walls having a depressed central portion with upwardly and inwardly facing surfaces that mate with the beveled surfaces, said central portion being of a width slightly less than the narrowest distance between the fillets and substantially less than the distance between the side walls below the fillets, said spanner terminating at each end in downwardly and outwardly oblique conducting portions on opposite sides of the cage that are each disposed at an angle approximately matching the angle of the oblique portion of the corresponding stationary contact member and each of which bears a movable contact facing a corresponding stationary contact, the contact faces of one movable and associated stationary contact being a flat face and a spherical face and the contact faces of the other movable and associated stationary contact being a flat face and a cylindrical face with the longitudinal axis of the cylinder transverse to the length of the spanner; and resilient bias means to bias the spanner toward the top of the cage.

4. In a switch contact assembly, the combination comprising: a vertically movable actuator having a contact cage comprising spaced side walls and a top extending therebetween, said top having downwardly and outwardly facing beveled seating surfaces along opposite lower sides thereof, said side walls having fillets on their inner faces immediately below the junction with the top which converge upwardly toward one another to taper the spacing between the side walls to a narrower dimension at the top; a pair of spaced stationary contact members on opposite sides of the cage each having a downwardly and outwardly oblique conducting portion disposed at an angle of approximately 15 to 30 degrees downwardly from a perpendicular to the path of the actuator, and terminating in a stationary contact; a movable contact spanner that is inserted in the cage and extends beneath the top and between the side walls and having a depressed central portion with upwardly and inwardly facing surfaces that mate with the beveled surfaces, said central portion being of a width slightly less than the narrowest distance between the fillets and substantially less than the distance between the side walls below the fillets, said spanner terminating at each end in downwardly and outwardly oblique conducting portions on opposite sides of the cage that are each disposed at an angle approximately matching the angle of the oblique portion of the corresponding stationary contact member and each of which bears a movable contact facing a corresponding stationary contact, the contact faces of one movable and associated stationary contact being a flat face and a spherical face and the contact faces of the other movable and associated stationary contact being a fiat face and a cylindrical face with the longitudinal axis of the cylinder transverse to the length of the spanner; and resilient bias means to bias the spanner toward the top of the cage.

5. In a switch contact assembly, the combination comprising: a vertically movable actuator having a contact cage; a pair of spaced stationary contact members on opposite sides of the'cage each having a downwardly and outwardly oblique conducting portion disposed at an angle of approximately 15 to 30 degrees downwardly from a perpendicular to the path of the actuator and terminating in a stationary contact; a movable contact spanner that is inserted in the cage, said spanner terminating at each end in downwardly and outwardly oblique conducting portions on opposite sides of the cage that are each disposed at an angle approximately matching the angle of 'the oblique portion of the corresponding stationary contact member and each of which bears a movable contact facing a corresponding stationary contact, the contact faces of one movable and associated stationary contact being a flat face and a spherical face and the contact faces of the other movable and associated stationary contact being a flat face and a cylindrical face with the longitudinal axis of the cylinder transverse to the length of the spanner; and resilient bias means to bias the spanner toward the top of the cage.

6. In a switch contact assembly, the combination comprising: a pair of spaced stationary contact members each having a downwardly projecting conducting portion that turns outwardly from the other contact member to terminate in a generally rectangular contact of relatively narrow width and extended length; a movable contact actuator movable toward and away from the stationary contact members which includes a contact cage disposed centrally of the stationary contact members;a movable contact spanner mounted by the contact cage which extends from opposite sides of the cage topresent generally rectangular contacts at its ends in alignment with the contacts of the stationary contact members; and a pair of upright channel shaped metallic members that are not electrically connected to the movable and stationary contacts, one closely disposed about the sides and outer end of each set of stationary and movable contacts to be in the direct path of an are moving outwardly therefrom, each such metallic member being spaced from the sides and outer end of its associated set of contacts a distance equal to approximately 0.4 to 1 times the maximum contact gap.

7. In a switch contact assembly, the combination comprising: a pair of spaced stationary contact members each having a downwardly projecting conducting portion that turns outwardly from the other contact member to terminate in a generally rectangular contact having a length to width ratio within the range of 8:7 to 7:6; a movable contact actuator movable toward and away from the stationary contact members which includes a contact cage disposed centrally of the stationary contact members; a movable contact spanner mounted by the contact cage which extends from opposite sides of the cage to present generally rectangular contacts at its ends in alignment with the contacts of the stationary contact members; and a pair of upright channel shaped metallic members that are not electrically connected to the movable and stationary contacts, one disposed about the sides and outer ends of each set of stationary and movable contacts to be in the direct path of an are moving outwardly therefrom, and said channel members beingdisposed at a distance from the sides and outer end of their associated sets of contacts of approximately 0.4 to 1 times the maximum contact gap.

8. In a switch contact assembly, the combination comprising: a vertically movable actuator having a contact cage comprising spaced side walls and a top extending therebetween, said top having downwardly and outwardly facing beveled seating surfaces along opposite lower sides thereof, said side walls having fillets on their inner faces immediately below the junction with the top which converge upwardly toward one another to taper the spacing between the side walls to a narrower dimension at the top; a pair of spaced stationary contact members on opposite sides of the cage each having a downwardly and outwardly oblique conducting portion terminating in a generally rectangular contact of relatively narrow width and extended length; a movable contact spanner that is inserted in the cage and extends beneath the top and between the side walls having a depressed central portion with upwardly and inwardly facing surfaces that mate with the beveled surfaces, said central portion being of a width slightly less than the narrowest distance between the fillets and substantially less than the distance between the side walls below the fillets, said spanner terminating at each end in downwardly and outwardly oblique conducting portions on opposite sides of the cage that are each disposed at an angle approximately matching the angle of the oblique portion of the corresponding stationary contact member and each of which bears a movable contact facing a corresponding stationary contact and of a rectangular configuration substantially identical to that of a corresponding stationary contact, the contact faces of one movable and associated stationary contact being a flat face and a spherical face and the contact faces of the other movable and associated stationary contact being a fiat fact and a cylindrical face with the longitudinal axis of the cylinder being transverse to the length of the spanner; resilient bias means to bias the spanner toward the top of the cage; and a pair of upright channel shaped members that are not electrically connected to the movable and stationary contacts, one closely disposed about the sides and outer end of each set of movable and stationary contacts, each of the channel shaped members being spaced from the sides and end of its associated set of contacts a distance equal to approximately 0.4 to 1 times the maximum contact gap and being in the direct path of arcs blown outwardly from its associated set of contacts.

9. In a switch contact assembly, the combination comprising: avertically movable actuator having a contact cage comprising spaced side walls and a top extending therebetween, said top having downwardly and ioutwardly facing beveled seating surfaces along opposite lower sides thereof, said side walls having fillets on their inner faces immediately below the junction with the top which converge upwardly toward one another to taper the spacing between the side walls to a narrower dimension at the top; a pair of spaced stationary contact members on opposite sides of the cage each having a downwardly and outwardly oblique conducting portion disposed at an angle of approximately 15 to 30 degrees downwardly from a perpendicular to the path of the actuator and terminating in a generally rectangular contact having a length to width ratio within the range from 8:7 to 7:6; a movable contact spanner that is inserted in the cage and extends beneath the top and between the side walls and having a depressed central portion with upwardly and inwardly facing surfaces that mate with the beveled surfaces, said central portion being of a width slightly less than the narrowest distance between the fillets and substantially less than the distance between the side walls below the fillets, said spanner terminating at each end in downwardly and outwardly oblique conducting portions on opposite sides of the cage that are each disposed at an angle approximately matching the angle of the oblique portion of the corresponding stationary contact member and each of which bears a movable contact facing a corresponding stationary contact and of a rectangular configuration substantially identical to that of a corresponding stationary contact, the contact faces of one movable and associated stationary contact being a fiat face and a spherical face and the contact faces of the other movable and associated stationary contact being a flat face and a cylindrical face with the longitudinal axis of the cylinder transverse to the length of the spanner; resilient bias means to bias the spanner toward the top of the cage; and a pair of metallic, upright channel shaped members that are not electrically connected to the movable and Stationary contacts, one disposed about the sides and outer end of each set of movable and stationary contacts each of the channel shaped members being in the direct path of arcs blown outwardly from its associated set of contacts and being spaced from the sides and outer ends thereof a distance of approximately 0.4 to 1 times the maximum contact gap therefrom.

10. In a switch contact assembly the combination comprising: a fully enclosed arc chamber having side walls, a top wall and a bottom wall; a pair of stationary contacts entering the chamber and presenting contact faces spaced from one another at the front and rear top of the chamber; a movable contact actuator entering an opening in the bottom wall with a close fit; a movable contact with a spanner carried by said actuator and bridging between said stationary contacts that is movable from a lower open position toward said stationary contacts for engagement therewith, said spanner having contact ends in alignment with said stationary contact faces; a cooling shield that is not electrically connected to the movable and stationary contacts and is of generally U-shape set on end and encircles the sides and outer ends of each stationary contact and associated spanner end together with the gap therebetween; said shield being spaced from the sides and outer ends of its associated contacts at a distance equal to approximately 0.4 to 1 times the maximum gap between the movable and stationary contacts; and the bottom of said chamber being spaced immediately beneath the movable contact spanner when in open position and immediately beneath the lower ends of each cooling shield.

11. In a contact assembly, the combination comprising: a contact carrier having a contact cage that is open along two opposite vertical sides and that has a pair of spaced, substantially parallel vertically rising side walls that extend between and define the open sides and a top extending between the side walls, said top having obliquely disposed downwardly and outwardly facing contact spanner seating surfaces extending between the side walls and above the open sides of the contact cage which form opposite lower surfaces for the top, and said side walls having sloping inner faces opposite one another that converge upwardly toward the top with a taper to thereby decrease the distance between the side walls in the vicinity of the top; a movable contact spanner inserted in the contact cage and upwardly and downwardly movable therein, said spanner having ends extending outwardly from the open sides of the contact cage and a center portion between the walls that is of a width that substantially matches the distance between the side walls at the narrow upper end of the taper and that is considerably less than the distance between the side walls at the wider lower terminus of the taper, said spanner further having upwardly and inwardly facing slanting surfaces extending outward from its center portion that mate with the contact spanner seating surfaces of the top when the spanner is in an upper position, said slanting surfaces being adapted to slide across the contact spanner seating surfaces of the top when the spanner is moved upwardly into engagement with the top to thereby align the spanner with the contact cage in an endwise direction, and said tapered inner surfaces of the side walls beingadapted to simultaneously align the spanner in a crosswise direction when it is moved upwardly; and bias means urging the spanner upwardly toward the top against which bias means the spanner may be moved downwardly to a position floating free of the side walls of the contact cage.

References Cited in the file of this patent UNITED STATES PATENTS 2,071,149 Wilms et al. Feb. 16, 1937 2,239,031 Bierenfeld et al Apr. 22, 1941 2,534,069 Schleicher Dec. 12, 1950 2,750,477 Brown et al. -June 12, 1956 2,924,685 Burch Feb. 9, 1960 FOREIGN PATENTS 1,059,538 Germany June 18, 1959 

10. IN A SWITCH CONTACT ASSEMBLY THE COMBINATION COMPRISING: A FULLY ENCLOSED ARC CHAMBER HAVING SIDE WALLS, A TOP WALL AND A BOTTOM WALL; A PAIR OF STATIONARY CONTACTS ENTERING THE CHAMBER AND PRESENTING CONTACT FACES, SPACED FROM ONE ANOTHER AT THE FRONT AND REAR TOP OF THE CHAMBER; A MOVABLE CONTACT ACTUATOR ENTERING AN OPENING IN THE BOTTOM WALL WITH A CLOSE FIT; A MOVABLE CONTACT WITH A SPANNER CARRIED BY SAID ACTUATOR AND BRIDGING BETWEEN SAID STATIONARY CONTACTS THAT IS MOVABLE FROM A LOWER OPEN POSITION TOWARD SAID STATIONARY CONTACTS FOR ENGAGEMENT THEREWITH, SAID SPANNER HAVING CONTACT ENDS IN ALIGNMENT WITH SAID STATIONARY CONTACT FACES; A COOLING SHIELD THAT IS NOT ELECTRICALLY CONNECTED TO THE MOVABLE AND STATIONARY CONTACTS AND IS OF GENERALLY U-SHAPE SET ON END AND ENCIRCLES THE SIDES AND OUTER ENDS OF EACH STATIONARY CONTACT AND ASSOCIATED SPANNER END TOGETHER WITH THE GAP THEREBETWEEN; SAID SHIELD BEING SPACED FROM THE SIDES AND OUTER ENDS OF ITS ASSOCIATED CONTACTS AT A DISTANCE EQUAL TO APPROXIMATELY 0.4 TO 1 TIMES THE MAXIMUM GAP BETWEEN THE MOVABLE AND STATIONARY CONTACTS; AND THE BOTTOM OF SAID CHAMBER BEING SPACED IMMEDIATELY BENEATH THE MOVABLE CONTACT SPANNER WHEN IN OPEN POSITION AND IMMEDIATELY BENEATH THE LOWER ENDS OF EACH COOLING SHIELD. 